Drawbored mortise & tenon question

I’m building my workbench base using mortise & tenon joinery, and was wondering about the best way to pin the joints. I’ll be using 1/2” maple dowels, and my question is whether there is any advantage or drawback to drill completely through both sides of the mortise for the drawbore (as opposed to a “blind” drawbore, if that makes sense…). Any guidance here is appreciated!

-- John, BC, Canada

11 replies so far

To drawbore you have to shave down one end of the peg to make sure it will go into the hole. If you drilled a through hole, you would have to pound the peg all the way through so the other side gets filled with your full diameter peg. It would probably work, but it may be more work than its worth if your legs are thick. Having a blind hole doesn’t require you to pound the peg as much.

I tried drawboring the legs on the workbench I just completed (build is blogged) and it didn’t go too well.

I couple of thoughts based on my attempt:

I wouldn’t try 1/2” dowels; I tried 3/8” and they were pretty damn stiff.

I also think I offset the holes too much, and the dowel couldn’t make it around the bends. Keep the offset to less than 1/16”.

You also need a lot of taper in the dowel, I made the end into a point, kind of like a thick pencil, and I don’t think that was nearly enough taper. I’d do a lot more taper if I tried again.

I also used pre-made dowel, and I had issues with it breaking while I was pounding. Pre-made dowels are just not all straight grain. Make your own dowels using straight grain stock.

My drill press didn’t have enough travel to go through the leg in one pass, so I drilled what I could in the press (bench top model) and then finished with a hand drill. I don’t think this helped. If I did it again I would likely seek out a real drill press so I knew everything was properly lined up.

You might want to try making the dowels a bit undersized if you go completely through the leg, it’s a lot of contact area and a lot of friction.

I had seen Marc’s video before, it’s actually what got me thinking about using the drawbore method.

I can envision all kinds of things going wrong with my attempt :) which is leading me to possibly just clamping the joints tight and pinning them with the dowels, rather than trying to offset the tenon bore. I’ve got high quality maple dowels, so I am not worried about breaking them, and my drill press will just get through the legs in one pass.

I guess I’m off to make some practice atempts in scrap… I’ve got too many hours into the project so far to screw it up now!

Worst case, you can drill through once you have them clamped and just pin them, if you aren’t having any luck getting them through. That’s what I ended up doing with about half of mine. It’s well worth a try!

Thanks John. When I watched Marc’s podcast I thought to myself that 1/16” offset seems an awful lot… will probably shoot for something much less aggresive myself. Btw, I just read through your workbench blog, nice job on that!

Thanks RGtools for that tip. However, I was planning to glue everything in place, including the pins. Is that a bad idea? I don’t plan on ever needing to disassemble the workbench. But then again, I am a rookie at this so maybe glue is not the right approach for this type of joint?

I have done things both ways (I tend to glue blind drawbores when I use them….might as well). The pins occassionally blow up when you strike them in…it’s nice to have a second pin ready to drive the first failed one through in that case (make an extra for each 4 you have to place…you won’t need that many but peace of mind is a good thing). No glue is really needed to hold these in based on the compression of the joint. What this does give you is an easier repair should your tenon fail for some reason 150 years down the road…

I think gluing the pins is indeed a bad idea. First, the down-side. you REALLY don’t want that glue binding up the pin as you drive it. For a drawbore to do its magic, you want it to be kinda hard for it to work its way around that bend. How hard? Not quite so hard that you break the pin. Any extra resistance is bad as it’ll increase the chances you break the pin. Now, for the up-side…. here’s the real issue. There’s no up-side to gluing that pin. There is no force present that will work the pin free. The pin never experiences any force along its length, so the glue would serve no purpose except to make it harder for you to assemble and repair.